Dysfunction of the ubiquitin-proteasome system (UPS) and autophagy, two main intracellular proteolytic pathways, have been observed in a variety of heart diseases and implicated in the genesis of congestive heart failure (CHF), the final common pathway for virtually all heart diseases and afflicting the life of millions of Americans. The COP9 signalosome (CSN) is an evolutionarily conserved protein complex consisting of 8 unique subunits (CSN1 ~ CSN8). In the preceding competitive cycle, we have discovered that the Csn8/CSN is required for not only UPS-mediated proteolysis but also autophagy to exert their protein quality control roles in mouse hearts. Perinatal cardiomyocyte-restricted CSN subunit 8 knockout (CR-Csn8KO) causes primarily massive cardiomyocyte (CM) necrosis in intact mice and this is preceded by impairment in the autophagic- lysosomal pathway and accompanied by UPS malfunction. The CR-Csn8KO mice develop dilated cardiomyopathy and die of CHF prematurely. Building upon these exciting novel findings, we propose to decipher the molecular mechanisms by which Csn8/CSN regulates the autophagic-lysosomal pathway and cardiomyocyte survival in the heart. Using a combination of innovative genetic manipulations and pharmacological interrogations in intact mice, we will pursue three specific aims to test the central hypothesis that Csn8/CSN promotes AM via Rab7 and facilitates PQC in CMs, thereby promoting CM survival by suppressing the RIP1/RIP3-mediated necrosis pathway. Specific aim 1 defines molecular mechanisms by which Csn8/CSN promotes autophagy. This will test the hypothesis that Csn8/CSN regulates autophagosome maturation (AM) via Rab7. Specific aim 2 investigates the pathophysiological significance of autophagic activation by proteasome inhibition. This is to test the hypothesis that proteasome functional insufficiency (PFI) activates cardiac autophagy and this activation compensates for protein quality control impairment caused by PFI. Specific aim 3 tests the hypotheses that impaired AM compromises the degradation of proteasome substrates and that the duo-impairment in the UPS and autophagy triggers CM necrosis via the RIP1-RIP3 mediated pathway. The completion of this research is expected to significantly improve our understanding on how protein quality control and degradation pathways in the heart are coordinately regulated, especially by the CSN, which will facilitate the search for new strategies to prevent and/or more effectively treat CHF, a leading cause of death and disability in the US. PUBLIC HEALTH RELEVANCE: Congestive heart failure is the final common pathway of virtually all heart disease and is the most expensive single diagnosis in US health care. It is a highly lethal and disabling syndrome. Despite recent advances in its clinical management, it remains the leading cause of death in the US. This research project will help improve our understanding on the molecular mechanisms underlying the progression of various heart diseases to congestive heart failure, which will ultimately facilitate the search for new measures to prevent or more effectively treat this common and yet life-threatening disorder.